Last night I found a specific planet I want and was colonizing and abandoning it to recolonize in an attempt to get 300+ fields. Was working just fine now today I come back to try some more and after abandoning it it wont let me recolonize like I was doing last night?

All planet has limited fields to build new buildings. Amount of fields calculates randomly on colonization. You may need several attempts of colonization/leaving planet till you get a good amount of fields.300+ fields is what you need, usually takes 5-7 attempts.

There is another way to increase fields. Building Terraformer, researching tech, hiring officer.But my advice it to colonize ~300 field`s planet and later use buildings and researching to make it bigger